In-situ recovery of hydrocarbons from underground formations of oil shale



3,228,468 RBONS FROM 101L SHALE Jan. 11, 1966 D. P. NICHOLS IN-SITURECOVERY OF HYDROCA UNDERGROUND FORMATIONS OF Filed Dec. 8. 196

United States Patent 0 ,228,463 IN-SITU RECOVERY OF ROCARBONS FROMUNDERGROUND FQRWATION OF OIL SHALE Dean P. Nichols, Dallas, Team,assignor to Socony' Mobil Git Company, inc, a corporation of New YorkFiled Dec. 8, 1961, Ser. No. 157,938 8 Ciaims. (Cl. 16.611)

This invention relates to a process for efficient recovery ofhydrocarbons from oil shale. More particularly, the present invention isdirected toward a process for in-situ retorting and recovery ofhydrocarbons from underground formations of oil shale. i

Vast deposits of oil shale are located within the United States and aregenerally disposed beneath the earths surface in underground formations.The oil shale in such deposits contains hydrocarbons known as kerogen.These hydrocarbons cannot be recovered by conventional petroleumproducing methods. Shale containing kerogen must be subjected toretorting or destructive distillation to provide shale oil, which is ahydrocarbon product much like crude petroleum and which may be processedto provide fuels and other useful products. Generally, a ton of oilshale can provide approximately 1 to 50 gallons of shale oil. Thus,these vast deposits of oil shale provide a significant reserve ofhydrocarbon materials. Economical production of shale oil from such vastoil shale deposits would be a tremendous contribution to this countrysnational wealth and provide a great supply of hydrocarbon materials inthe event of a national emergency.

Up to the present time no known process for recovering the shale oilfrom oil shale formations has produced shale oil that, from an economicstandpoint, could be reasonably compared to petroleum crude oil.

One such known method for recovering the shale oil is to useconventional mining methods to remove the oil shale from the undergroundformations Where it resides. At the surface, the oil shale is crushedinto a size suitable for retorting and is then subjected to retorting.The high costs of such operations in conjunction with the small amountsof shale oil produced prevent utilization of this method on a commercialscale.

Other methods heretofore proposed have been directed toward in-siturestorting of the oil shale to decompose the kerogen therein andeducting the hydrocarbon products, i.e., shale oil. Although suchprocesses have avoided some of the expensive conventional mining costs,they are unsatisfactory for one or more reasons from the standpoint ofcommercial operations. One of these reasons is the low naturalpermeability of oil shales. Because of this, complicated tunneling andpreparation of small isolated units in the oil shale formation have beenrequired to provide sufiicient permeability to permit heating the oilshale by passing heated or combustible gases therethrough to drive outthe shale oil. Although some processes utilize fracturing of the oilshale, the resultant production of crevices in the oil shale formationhas been limited to an extent insufficient to create the requiredpermeability for eificient and relatively complete recovery of thehydrocarbons from the oil shale.

The present invention is directed toward a process for the in-situretorting and recovery of hydrocarbons from underground formations ofoil shale that overcomes the difficulties existing in known processesand which can be used commercially. Further, the process of thisinvention prepares the oil shale, by extensive and complete fracturing,to the desired degree of permeability to facilitate the ready heatingthereof in order to release and drive the hydrocarbons from the oilshale to a common collection area with only a minimum of costly conven-"ice tional mining operations incurred. In addition, the present processdoes not depend upon specially disposed formations or highlypor o-usadjacent stratum or fissures for its efiicient operation but can usesuch naturally occurring structures to great advantage in any oil' shaleformation.

It is therefore an object to the present invention to provide a processfor in-si tu retorting and recovery of hydrocarbons from an undergroundformation of oil shale with greater facility, with maximum recovery ofhydrocarbons, and at lower costs than in known processes.

Another object is to provide a process for in-situ retorting andrecovery of hydrocarbons from an underground formation of oil shalewherein greater permeability and also more homogeneous permeability isprovided to facilitate permeation of such formation with heat sufficientto drive substantial quantities of hydrocarbons from the oil shale formore completerecovery of such hydrocarbons. 4 i

Yet another object is to provide a process in accordance with thepreceding objects wherein naturally occurring fissures and permeablestrata areused to great advantage in recovery of hydrocarbons containedin oil shales.

A further object is to provide a process for in-situ restorting andrecovery of hydrocarbons from an underground formation of oil shale thatachieves greater efficiency than prior processes by utilizinghydrocarboncontaining materials derived in practicing such process andproducts produced by such'process as sources of heat and eductive agentsto assist inremoving the hydrocarbons from the shale.

Another further object is to provide a process for insitu retorting andrecovery of hydrocarbons from underground formations of oil shalewherein all openings introduced into said shale formation may beutilized for a dual functioning in such process so that greaterefliciency in such process is obtained.

Theseand other objects will become more apparent when read inconjunction with the following detailed description and the attacheddrawings wherein:

FIG. 1 shows an illustrative embodiment of the application of theprocess of the present invention to an underground formation of oilshale with the view taken in vertical section through the earth; and

FIG. 2 is a section taken on line 22 of FIG. 1.

The objects are achieved by the process comprising the steps ofsurrounding a desired portion of the oil shale formation with ahorizontally or nearly horizontally disposed tunnel. At least oneborehole is provided leading substantially vertically from the earthssurface downwardly into the portion of the shale formation surrounded bythe tunnel. The oil shale formation disposed about the vertical boreholeis fractured as described hereinafter to a degree providing the desiredpermeability for efficient retor-ting of the formation. After fracturingof the oil shale formation, a heat creating gas is injected into thefractured shale formation through the borehole to heat the oil shaleformation from adjacent the borehole progressively outwardlytoatemperature sufficient to drive the hydrocarbons contained therein awayfrom the borehole and into the tunnel. The recovered hydrocarbonscollected in the tunnel are removed to complete the process in its basicconcept. Other aspects of the present invention permit additional stepsto be incorporated therein to provide certain advantageous results aswill be apparent as this description proceeds.

Referring now to the drawings, a detailed description of oneillustrative embodiment of the present invention will now be given. InFIG. I, the oil shale underground formation is designated by numeral 10and has superimposed an overburden 11 and resides on a more or lessimpervious substrata 12. i

The oil shale in formation 10 usually occurs in horizontal or nearlyhorizontal beds as shown and varies in thickness from fractions of afoot to hundreds of feet. The oil shale formation 10 may haveinterspersed one or more highly permeable strata such as a permeable bed13 residing more or less parallel to the bedding plane of the oil shaleformation. Additionally, natural vertical or nearly vertical fissures14, 15, 16, 17, and 18 may be found in oil shale formation 10.

A portion of the oil shale formation 10 from which recovery of thecontained hydrocarbon is desired is surrounded by a horizontally ornearly horizontally disposed tunnel 19. This portion of the formation 10will be hereinafter referred to as surrounded oil shale and isdesignated by numeral 10a. The tunnel 19 has a vertical dimensiongenerally equal to the thickness of the oil shale to be processed and isconnected to the earths surface by a passageway 20 which serves as ameans of access to form the tunnel, an exit through which the tunnelingdebris is removed, and, later, a place to position apparatus forremoving recovered hydrocarbons from the tunnel. Passageway 20 mayextend somewhat below the fioor 21 of the tunnel to form a centralcollection area for the hydrocarbons driven from the oil shale. Whilethe surrounded oil shale 10a is shown as rectilinear in section, suchshape is merely for illustrative purposes and the use of other shapesmay be used with equal facility and advantage.

Where the permeability of the overburden 11 or substrata 12 is greatenough to provide undesired avenues of escape for the loss of shale oilfrom the formation surrounded by the tunnel and from the tunnel, layersof the relatively nonporous oil shale may be allowed to remain adjacentthe overburden or the substrata. Naturally, such remaining layers of oilshale can be used as roof supporting means to support the overburden 11.Similarly, the portion of the oil shale selected to be processed forrecovery of hydrocarbon may be disposed in a position completelysurrounded by the remainder of the oil shale formation 10.

Generally the size of the tunnel and the portion of the oil shale 10asurrounded therewith will depend upon the efiiciency of the mode offracturing utilized and the cost of constructing the tunnel 19.

A plurality of boreholes are provided into the surrounded oil shale 10aand any suitable means such as conventional boring apparatus can be usedto provide the boreholes as will be apparent to one skilled in the art.At least one borehole 22 is provided in the oil shale 10a. The borehole22 is substantially vertical with respect to the earths surface andextends from the surface into the surrounded oil shale 10a. The boreholemay extend to a depth partially or completely through oil shale 10a, oreven to pass below it into the substrata 12 depending upon theconditions surrounding the oil shale a. Preferably a plurality of suchboreholes 23 through 30 are provided and are disposed in quantity anddisposition in the surrounded oil shale 10a whereby substantiallycomplete fracturing of such shale by a fracturing means operated fromthe boreholes can be obtained. Where naturally occurring verticalfissues are present, one or more of the boreholes may be placed closelyadjacent or intersecting such fissures so that upon fracturing crevices40 are created in the oil shale in communication with the fissures. Thisis an important advantage in utilizing naturally occurring porousstructures to provide greater and more homogeneous permeabilitythroughout the oil shale from which hydrocarbons are to be recovered.

In an oil shale formation having a small vertical dimension, verticalboreholes may be suflicient to obtain extensively complete fracturing ofsuch formation. However, horizontally disposed boreholes may be usedwhere the formation is of a significant vertical dimension such thatfracturing from the vertical boreholes is insufficient to provide thedesired permeability. They may also be used for other reasons such asutilization of the horizontal permeable bed 13 to assist in eduction ofthe hydrocarbons driven from the oil shale.

In such instances it may be desirable to provide at least one borehole31 from tunnel 19 into the oil shale 10a that is substantiallyhorizontal. Preferably a plurality of such horizontal boreholes 32through 38 are provided in the surrounded oil shale 10a. Similarboreholes are provided in the lower portion of the surrounded oil shale10a below permeable bed 13 as shown in FIG. 1. The quantity anddisposition of such boreholes provided in the oil shale formation aresuch as to permit fracturing of the formation to a desired degree andextent of homogeneous permeability. Where a naturally occurring, highlypermeable stratum, such as permeable bed 13, is present, it can be usedas a ready avenue of eduction for the hydrocarbons driven from the oilshale and for their conveyance to tunnel 19. In such cases, at least oneand preferably a plurality of the horizontal boreholes are placedclosely adjacent such naturally permeable stratum. Upon fracturing byfracturing means operated from such boreholes, extensive crevices 41 arecreated in the oil shale formation which are in communication with thepermeable bed 13. Crevices 41 are shown in a broken section centrallylocated in FIG. 1.

In some cases it may be desirable to complete tunnel 19 before thedrilling of boreholes into the surrounded oil shale 10a. However, it isintended to be within the scope of this invention that the particularorder of providing boreholes is not contingent upon their being vertical or horizontal nor upon the completion of tunnel 19 but rather willbe determined by the conditions present in the oil shale formation.

The positions of the naturally porous structures such as fissures andpermeable beds may be determined by observations made in constructingtunnel 19 or by coring operations.

The surrounded oil shale 10a is extensively fractured through the use ofa fracturing means operated through the boreholes. Any suitablefracturing means can be used such as explosives or hydraulic means.Fracturing from the vertical boreholes will produce crevices 40 whichcan generally extend radially outwardly as shown in FIGS. 1 and 2.Fracturing from the horizontal boreholes can produce crevices 41 whichgenerally extend radially outwardly as shown in a broken sectioncentrally of FIG. 1 and also in FIG. 2. Preferably crevices 40 and 41 atleast in part intersect and also intersect with the naturally porousstructures present such as fissues 14 through 18 and permeable bed 13whereby greater and more homogeneous permeability is obtained in the oilshale. This is an important advantage of the present invention thatpermits uniform, thorough heating of the oil shale formation and readyeduction of the hydrocarbons therefrom into tunnel 19 for maximumefficient recovery of the hydrocarbons.

Fracturing of the surrounded oil shale 10a facing the tunnel 19 may bealso achieved as part of the formation of such tunnel, or later, throughthe use of explosives, and provides crevices 42 extending inwardly intothe shale. Other fracturing means can be used if desired.

After fracturing, the oil shale formation must be subjected to heatingto decompose kerogen into hydrocarbons. Preferably, heating is totemperatures of the kerogen above 650 F. The fractured oil shale isheated to a temperature sufficient to heat the surrounded oil shale 10ato drive the hydrocarbons therefrom and into the tunnel 19 Where theyare collected for recovery. Because of extensively complete fracturingof the surrounded oil shale 10a, ready heating thereof to drive andeduct the hydrocarbons is obtained by the relatively free passage of aheat creating gas through the created and natural crevices.

The term heat creating gas is used herein to include a gas selected fromthe group consisting of oxygen containing gases singly or in variousproportions and combinations with combustible and noncombustible gases.

The surrounded oil shale a is heated by injecting a heat creating gasthrough one or more of the vertical boreholes such as borehole 22 sothat the oil shale is heated to the required temperature. The heatcreating gas having oxygen containing gases may be preheated initiallyat the surface by suitable equipment to a temperature sufticient toignite spontaneously a portion of the hydrocarbon materials in theshale. The combustion of such materials produces heat to decompose theherogen and to drive the resultant hydrocarbon products from the shale.The heating begins with the shale adjacent the borehole and as the flamefront migrates through the formation, the heating moves progressivelyoutwardly from the borehole so as to provide a uniform heat front todrive the hydrocarbon products from the shale and into the tunnel 19.The vertical boreholes not used in the heating of the fractured oilshale formation are sealed or shut in so that only the outlets availablefor removal of recovered hydrocarbons from tunnel 19 to the earthssurface are one or more passageways 29.

Once the combustion of the oil shale is initiated, the temperature andthe velocity of the heat front can be regulated by adjusting thetemperature of the heat creating gas being introduced or the volume ofsuch gas or its oxygen content to a degree best suited for maximumrecovery of the hydrocarbons from the shale.

In some instances, such as when the hydrocarbon content of the oil shaleis relatively low or for other reasons, combustible gases may also beinjected into the surrounded oil shale 18a and therein ignited. Suchcombustible gases can provide the only fuel used for heating the shaleor to supplement the hydrocarbons used as natural fuel in such shale.The combustible gases may be injected into the shale through one or moreof the vertical boreholes, separately or in combination with oxygencontaining gases. It may be found desirable in certain aspects ofoperation to alternately inject the oxygen containing gases and thecombustible gases into the surrounded oil shale 18a. Noncombustiblegases may be admixed with the injected gases to assist in controllingthe temperature of the flame front. Alternatively, such gases may beheated to temperatures sufiicient to decompose the kerogen in the oilshale and to facilitate the recovery of hydrocarbons therefrom and usedseparately or in combination with the previously mentioned gases. Theselection of any particular mode of injection of the heat creating gaswill depend upon the conditions existing in the shale formation. Thisstep of in-situ heating by injecting various gases is well known tothose skilled in the art.

Because of the greater and more homogeneous permeability of thefractured oil shale, the heating of the oil shale is readily achievedand, further, the heating is under the most ideal conditions. This is asa result of moving a heating front radially outwardly from one or morecentral locations toward a peripheral collection Zone. There is thusprovided maximum recovery of hydrocarbons from the shale.

Further efficiency in heating is obtained by the heat creating gaspassing through hot shale from which hydrocarbons have been removed soas to provide preheating of such gas.

The hydrocarbons driven from the surrounded oil shale Ida flow throughthe crevices in the fractured oil shale, the natural fissures andpermeable beds present, and also the horizontal boreholes 31 through 38to collect in tunnel 19 for convenient recovery.

Obviously, an advantage of the present process is that the passageway20, the boreholes and the tunnel 19 are used for dual purposes, both toprepare the oil shale formation to the desired degree and extent ofhomogeneous permeability and to facilitate the recovery of thehydrocarbons.

The hydrocarbons driven from the oil shale formation collect in tunnel19 and are recovered therefrom by suitable conventional liquid and vaporphase collection apparatus. Such apparatus is illustratively shown inFIG. 1 by conduits 43 and 44 extending downwardly through passageway 20into tunnel 19. Conduit 43 extends into the lowest level of tunnel 19.for removing the liquid phase of the recovered hydrocarbons and conduit44 spaced therefrom is provided for removing the vapor phase of suchrecovered hydrocarbons. The conduits may be connected at the earthssurface to conventional recovery and processing apparatus.

The efficiency of this process may be further increased by retorting atleast a portion of the rubble and cuttings produced by formation oftunnel 19 on the earths surface to produce hydrocarbon-containingmaterials in liquid andgaseous phases. A portion of the gaseous phasecan be admixed with the heat creating gas to be injected through thevertical borehole 22 as an additional fuel source to assist in heatingthe fractured shale formation. The gaseous phase can be also injectedinto the formation through one or more vertical boreholes other thanused for injecting the heat creating gas such as borehole 23 to providean additional fuel supply in the oil shale for heating same and also topromote more rapid eduction of the released hydrocarbons from thesurrounded oil shale 149a into the tunnel 19. The gaseous phase of therecovered hydrocarbons can be utilized in a similar manner to thegaseous phase of the retorted rubble and in either instance with orwithout separation of their noncombustible constituents.

The fracturing of the surrounded oil shale 19a by use of the variousboreholes may be adjusted to the schedule best suited forexpediting thein-situ heating of such shale formation. Thus, the formation disposedabout a row of boreholes, vertical or horizontal, along a given line maybe fractured and in-situ combustion inaugurated before proceeding withfracturing operations in the other boreholes.

For example, the formation disposed about one or more of the horizontalboreholes, if such are used, may be fractured along with the formationdisposed about the row of vertical boreholes Z2, 23, and 24. 'In-situheating is initiated by injection of a heat creating gas through one ormore of the vertical boreholes in such row before fracturing theformation disposed about one or more of the remaining Verticalboreholes. Alternatively, the formation disposed about any one, or anygroup, or all of such vertical boreholes may be fractured before insituheating by gas injection is initiated.

The selection and scheduling of the fracturing and injection operationsrelative to individual boreholes will be determined by the conditionspresent in specific oil shale formations. It is envisioned to be withinthe scope of the present invention that different and flexiblearrangements both as to selection and scheduling of the fracturing andgas injection operations relative to particular boreholes can be made tosecure maximum recovery of shale oil from individual oil shaleformations.

Upon completion of the desired recovery of hydrocarbons from thetunnel-surrounded oil shale, tunnel 19 may be extended to enclose a newadjacent portion of the oil shale formation whereupon the novel processof this invention is utilized to recover the hydrocarbons therein.

The use by the present invention of extensive, readily producedboreholes and extensive fracturing reduces drastically the amount ofcostly conventional mining required for maximum recovery of hydrocarbonsfrom oil shale. In particular, the use of conventional rotary surfaceequipment can readily and economically produce the vertical boreholesrequired. Similarly, other known equipment is available for readilyproviding the horizontal boreholes.

It will be readily appreciated from the foregoing description thatherein is fully disclosed a novel process Well adapted to obtain maximumrecovery of hydrocarbons from underground formations of oil shale and toobtain such hydrocarbons economically and that this process may beextensively used as a means to produce vast quantities of hydrocarbons.

It will be understood that certain features and subcombinations are ofutility and may be employed Without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many embodiments as possible may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. The process of recovering hydrocarbons from un derground formationsof oil shale comprising the steps of:

(a) surrounding a portion of an oil shale formation with a horizontallydisposed tunnel,

(b) providing a plurality of boreholes to said surrounded shaleformation wherein at least one said borehole is substantially verticalwith respect to the earths surface and extends from such surface intosaid surrounded shale formation and at least one said borehole issubstantially horizontal and extends from said tunnel into saidsurrounded shale formation, said boreholes being spaced apart from oneanother a sufficient distance along their extent in the formation toexclude direct interconnection between any vertical and horizontalboreholes,

(c) fracturing the surrounded shale formation disposed about saidsubstantially vertical and horizontal boreholes,

(d) injecting a heat creating gas through said substantially verticalborehole into said fractured shale formation to heat said shaleformation from adjacent said borehole progressively outwardly to atemperature sufficient to drive the hydrocarbons contained in saidsurrounded shale formation away from said borehole and into said tunnel,and

(e) removing the recovered hydrocarbons from said tunnel.

2. The process of recovering hydrocarbons from underground formations ofoil shale comprising the steps of:

(a) surrounding a portion of an oil shale formation with a horizontallydisposed tunnel,

(b) providing a plurality of boreholes to said surrounded shaleformation wherein at least one said borehole is substantially verticalwith respect to the earths surface and extends from such surface intosaid surrounded shale formation and at least one said borehole isdisposed closely adjacent a naturally occurring permeable structurepresent within said surrounded shale formation, said boreholes beingspaced apart from one another a sufficient distance along their extentin the formation to exclude direct interconnection between any verticaland horizontal boreholes,

(c) fracturing the surrounded shale formation disposed about saidboreholes to provide a multitude of crevices at least in part connectingsaid boreholes with said naturally occurring permeable structure,

(d) injecting a heat creating gas through one substantially verticalborehole into said fractured shale formation to heat same from adjacentsaid borehole progressively outwardly to a temperature sufficient todrive the hydrocarbons contained in said surrounded shale formation awayfrom said borehole and into said tunnel, and

(e) removing the recovered hydrocarbons from said tunnel.

3. The process of claim 2 wherein said borehole adjacent a naturallyoccurring permeable structure is substantially vertical with respect tothe earths surface.

4. The process of claim 2 wherein said borehole adjacent a naturallyoccurring permeable structure is substantially horizontal and extendsfrom said tunnel into said surrounded shale formation.

5. The process of recovering hydrocarbons from underground formations ofoil shale comprising the steps of:

(a) surrounding a portion of an oil shale formation with a horizontallydisposed tunnel,

(b) providing a plurality of boreholes to said surrounded shaleformation wherein at least one said borehole is substantially verticalwith respect to the earths surface and extends from such surface intosaid shale formation closely adjacent a vertically extending naturalfissure and at least one said borehole is substantially horizontal andextend from said tunnel into said surrounded shale formation closelyadjacent a natural permeable stratum, said boreholes being spaced apartfrom one another a sufficient distance along their extent in theformation to exclude direct interconnection between any vertical andhorizontal boreholes,

(c) fracturing the surrounded, shale formation disposed about saidboreholes to provide a multitude of crevies at least in part connectingsaid boreholes with one another and said fissure and said permeablestratum present in said shale formation,

((1) injecting a heat creating gas through one vertical borehole intosaid fractured shale formation to heat same from adjacent said boreholeprogressively outwardly to a temperature sufficient to drive thehydrocarbons contained in said surrounded shale formation away from saidborehole and into said tunnel, and

(e) removing the recovered hydrocarbons from said tunnel.

6. The process of recovering hydrocarbons from underground formations ofoil shale comprising the steps of:

(a) surrounding a portion of an oil shale formation with a horizontallydisposed tunnel,

(b) providing a plurality of substantially vertical boreholes to saidshale formation wherein said boreholes extend from the earths surfaceinto said surrounded shale formation,

(c) fracturing the surrounding shale formation disposed about one ofsaid vertical boreholes, and injecting a heat creating gas through saidsubstantially vertical borehole into said fractured shale formation toheat said shale formation from adjacent said borehole progressivelyoutwardly to a temperature sufficient to drive the hydrocarbonscontained in said surrounded shale formation away from said borehole andinto said tunnel,

(d) thereafter fracturing the surrounded shale formation disposed arounda second. of said substantially vertical boreholes and injecting a heatcreating gas through said substantially vertical borehole into saidfractured shale formation to heat said shale formation from adjacentsaid second borehole progressively outwardly to a temperature sufficientto drive the hydrocarbon contained in said surrounded shale formationaway from said second borehole and into said tunnel, and

(e) removing the recovered hydrocarbons from said tunnel.

7. The process of recovering hydrocarbons from un- 65 dergroundformations of oil shale comprising the steps of: (a) surrounding aportion of an oil shale formation with a horizontally disposed tunnel,

(b) providing at least one borehole to said surrounded shale formationwhich borehole is substantially vertical with respect to the earthssurface and extends from such surface into said shale formation,

(0) fracturing the surrounded shale formation disposed about saidborehole,

(d) injecting a heat creating gas through said borehole into saidfractured shale formation to heat said shale formation from adjacentsaid borehole progressively outwardly to a temperature sufficient todrive the hydrocarbons contained in said surrounded shale formation awayfrom said borehole and into said tunnel, and

(e) retorting on the earths surface at least a portion of the rubble andcuttings produced by formation of the tunnel surrounding said shaleformation to produce hydrocarbon-containing materials in liquid andgaseous phases,

(f) injecting a portion of said gaseous phase through a verticalborehole other than that used for injecting said heat creating gas intothe fractured shale formation to provide additional fuel to heat saidshale formation and to promote more rapid eduction of hydrocarbons fromthe fractured shale formation into the tunnel, and

(g) removing the recovered hydrocarbons from said tunnel.

8. The process of recovering hydrocarbons from underground formations ofoil shale comprising the step of:

(a) surrounding a portion of an oil shale formation with a horizontallydisposed tunnel,

(b) providing a plurality of boreholes to said surrounded shaleformation wherein at least one said borehole is substantially verticalwith respect to the earths surface and extends from such surface intosaid surrounded shale formation and at least one said borehole issubstantially horizontal and extends from said tunnel into saidsurrounded shale formation,

(c) fracturing the surrounded shale formation disposed about saidubstantially vertical and horizontal boreholes,

(d) injecting a heat creating gas through said substantially verticalborehole into said fractured shale formation to heat said shaleformation from adjacent said borehole progressively outwardly to atemperature suflicient to drive the hydrocarbons contained in saidsurrounded shale formation away from said borehole and into said tunnel,

(e) retorting on the earths surface at least a portion of the rubble andcuttings produced by formation of the tunnel surrounding said shaleformation to produce hydrocarbon-containing materials in liquid andgaseous phases,

(f) injecting a portion of said gaseous phase through a verticalborehole other than that used for injecting said heat creating gas intothe fractured shale formation to provide additional fuel to heat saidshale formation and to promote more rapid eduction of hydrocarbons fromthe fractured shale formation into the tunnel, and

(g) removing the recovered hydrocarbons from said tunnel.

References Cited by the Examiner UNITED STATES PATENTS 1,269,747 6/1918Rogers 166-39 2,481,051 9/1949 Uren 166-39 X 2,642,943 6/1953 Smith etal. 16611 2,780,449 2/1957 Fisher et al. 16611 2,788,071 3/1957 Pelzer16611 2,801,089 7/1957 Scott 16611 X 2,901,043 8/1959 Campion et al.166-11 2,970,826 2/1961 Woodruff 166-11 X 3,026,937 3/1962 Simm 16611 XCHARLES OCONNELL, Primary Examiner.

35 BENJAMIN HERSH, Examiner.

6. THE PROCESS OF RECOVERING HYDROCARBONS FROM UNDERGROUND FORMATIONS OFOIL SHALE COMPRISING THE STEPS OF: (A) SURROUNDING A PORTION OF AN OILSHALE FORMATION WITH A HORIZONTALLY DISPOSED TUNNEL, (B) PROVIDING APLURALITY OF SUBSTANTIALLY VERTICAL BOREHOLES TO SAID SHALE FORMATIONWHEREIN SAID BOREHOLES EXTEND FROM THE EARTH''S SURFACE INTO SAIDSURROUNDED SHALE FORMATION, (C) FRACTURING THE SURROUNDING SHALEFORMATION DISPOSED ABOUT ONE OF SAID VERTICAL BOREHOLES, AND INJECTING AHEAT CREATING GAS THROUGH SAID SUBSTANTIALLY VERTICAL BOREHOLE INTO SAIDFRACTURED SHALE FORMATION TO HEAT SAID SHALE FORMATION FROM ADJACENTSAID BOREHOLE PROGRESSIVELY OUTWARDLY TO A TEMPERATURE SUFFICIENT TODRIVE THE HYDROCARBONS CONTAINED IN SAID SURROUNDED SHALE FORMATION AWAYFROM SAID BOREHOLE AND INTO SAID TUNNEL, (D) THEREAFTER FRACTURING THESURROUNDED SHALE FORMATION DISPOSED AROUND A SECOND OF SAIDSUBSTANTIALLY VERTICAL BOREHOLES AND INJECTING A HEAT CREATING GASTHROUGH SAID SUBSTANTIALLY VERTICAL BOREHOLE INTO SAID FRACTURED SHALEFORMATION TO HEAT SAID SHALE FORMATION FROM ADJACENT SAID SECONDBOREHOLE PROGRESSIVELY OUTWARDLY TO A TEMPERATURE SUFFICIENT TO DRIVETHE HYDROCARBONS CONTAINED IN SAID SURROUNDED SHALE FORMATION AWAY FROMSAID SECOND BOREHOLE AND INTO SAID TUNNEL, AND (E) REMOVING THERECOVERED HYDROCARBONS FROM SAID TUNNEL.